Single 18" HDC3 for now.. Might be a little longer than I thought to buy the 2nd 18".
Truck bed is 19" tall, 60" wide, 17" long, then 50" between wheel wells to work with. Im guessing 38hz would be good for the HDC3.
Im guessing 4th order would be best for me because I don't want to cut a 15"+ hole out of the cab. But I don't have da mad skillz to design a 4th order..